Human beings subjected to high ambient acoustic noise environments can suffer a variety of negative effects, such as degraded ability to perform tasks or inability to sleep.
Several techniques exist to reduce the effects of ambient noise. For instance, sound absorbing material can surround the ears or be inserted in the ear canal, typically achieving 20 to 30 dB reduction of external sounds. Passive noise attenuation can be supplemented by combining absorptive materials with an acoustic transducer, such as a miniature speaker. The transducer is used to produce sounds which may be designed to actively cancel residual noise at the ear, or to provide sounds which are designed to conceal the external noise through the psychoacoustic phenomenon of masking, where one sound prevents the perception of another. A masking signal as typically implemented can achieve a total perceived noise suppression of up to 70 dB in combination with sound absorption materials alone or sound absorption plus active cancellation.
The present invention describes a technique for improving the performance of audio waveforms generated specifically for sound masking.